1. Field of the Invention
This invention is related to methods and compositions for bringing about skin pigmentation and/or for causing skin depigmentation. More particularly, this invention relates to compounds which affect melanogenesis and can be used as depigmenting agents or as agents for darkening skin.
2. Background of the Invention
Skin coloring has been of concern to human beings for many years. In particular, the ability to remove hyperpigmentation, such as found in age spots, freckles or aging skin generally, is of interest to individuals desiring a uniform complexion. In certain areas of the world, general body whitening is desirable. There are also hypopigmentation and hyperpigmentation disorders that are desirable to treat. Likewise, the ability to generate a tanned appearance without incurring photodamage due to solar radiation is important to many individuals. There have been many methods proposed to accomplish depigmentation, as well as to accomplish darkening of the skin. For example, kojic acid, hydqinone, retinoids and other chemical compounds have been used for depigmentation. Dihydroxyacetone and like chemical compounds have been utilized for their ability to xe2x80x9ctanxe2x80x9d the skin without exposure to the sun.
Many of these previous solutions have not been found acceptable. There is often a distinct line of demarcation between the areas of skin to which such previous compositions have been applied. Therefore, precise application of all these compounds is necessary in order to achieve the desired result. Many of these compounds have been found to be quite irritating to the skin and therefore undesirable for use.
The understanding of the chemical and enzymatic basis of melanogenesis is heavily documented. Melanocytes migrate from the embryonal neural crest into the skin to produce secretory granules, melanosomes, which produce melanin. Melanogenesis occurs within the melanosome, and the melanin is later distributed to keratinocytes via the melanocyte dendrites. The key enzyme in melanogenesis is tyrosinase, which initiates a cascade of reactions which convert tyrosine to the biopolymer melanin. Two tyrosinase-related proteins (TRP""s) are known, TRP-1 and TRP-2. These proteins share with tyrosinase about 40% homology and have catalytic activities as well as regulatory roles in melanogenesis. TRP-1 is the most abundant glycoprotein in melanocytes.
In spite of the fact that the chemical and enzymatic basis of melanogenesis is well-documented, its regulation at the cellular level is only partially understood. Tyrosinase and the TRP""s share structural and biological properties with the lysosomal-associated membrane protein (LAMP) gene family, therefore their targeting to the melanosomal membrane might induce their activation. A phosphorylation/dephosphorylation reaction at the cytoplasmic tails of these proteins could be involved in the regulation of melanogenesis. The beta isoform of the Protein Kinase C (PKC) family has been shown to regulate human melanogenesis through tyrosinase activation. Gene expression of tyrosinase, TRP-1 and TRP-2 is coordinated. All three enyzmes are expressed in human epidermis. In melanocytes co-cultured with keratinocytes, these transcripts are expressed at a ratio of 45:45:10, respectively. In melanocytes cultured alone, only TRP-1 transcripts are present, indicating that a kerainocyte-derived signal is involved in the coordinate expression of these genes. The regulation of keratinocyte-melanocyte interactions and the mechanism of melanosome transfer into keratinocytes are not yet understood.
The Protease-activated receptor-2 (PAR-2) is a seven transmembrane G-protein-coupled receptor, that is related to, but distinct from the thrombin receptors (TR also named PAR-1, and PAR-3) in its sequence. Both receptors are activated proteolytically by an arginine-serine cleavage at the extracellular domain. The newly created N-termini then activate these receptors as tethered ligands. Both receptors could be activated by trypsin, but only the TRs are activated by thrombin. Only PAR-2 is activated by mast cell tryptase. Both receptors could also be activated by the peptides that correspond to their new N-termini, independent of receptor cleavage. SLIGRL, the mouse PAR-2 activating peptide, is equipotent in the activation of the human receptor. While the function of the TR is well documented, the biology of the PAR-2 has not yet been fully identified. A role for PAR-2 activation in the inhibition of keratinocyte growth and differentiation has been recently described (Derian et al., xe2x80x9cDifferential Regulation of Human Keratinocyte Growth and Differentiation by a Novel Family of Protease-activate Receptorsxe2x80x9d, Cell Growth and Differentiation, Vol. 8, pp. 743-749, July 1997).
In accordance with this invention, we have found a method for affecting changes in mammalian skin pigmentation comprising topically applying to the skin of a mammal a compound which affects the PAR-2 pathway. The compositions of this invention may contain one or more compounds that act as trypsin, as tryptase, as serine protease or as PAR-2 agonists, for increase in pigmentation. Alternatively, they may contain one or more compounds that act as serine protease inhibitors, trypsin inhibitors, thrombin inhibitors, tryptase inhibitors, as PAR-2 pathway inhibitors or as a PAR-2 antagonist for decrease in pigmentation, or xe2x80x9cdepigmentationxe2x80x9d.
As used herein, xe2x80x9cmammalxe2x80x9d means any member xe2x80x9cof the higher vertebrate animals comprising the class xe2x80x9cMammaliaxe2x80x9d, as defined in Webster""s Medical Desk Dictionary 407 (1986), and includes but is not limited to humans. As used herein, xe2x80x9creceptorxe2x80x9d shall include both intracellullar and extracellular receptors and shall mean those molecules capable of receiving and transducing a signal. The term PAR-2 refers to the protease-activated receptor-2 or a related protease activated receptor. The Protease-activated receptor-2 (hereinafter, xe2x80x9cPAR-2xe2x80x9d) is a serine-protease activated receptor that is expressed in numerous tissues, including keratinocytes and fibroblasts. The thrombin receptor (also named PAR-1, hereinafter, xe2x80x9cTRxe2x80x9d) is a serine-protease activated receptor that is expressed in numerous tissues, including keratinocytes. The biological roles of PAR-2 and TR in skin are not entirely known. However, we have found that interactions between keratinocytes and melanocytes, via the PAR-2 pathway, affect melanogenesis. We have found that thrombin inhibitors, and/or tryptase inhibitors, and/or trypsin inhibitors and PAR-2 antagonists can be used as depigmenting agents without irritation of the skin. PAR-2 agonists and serine proteases such as trypsin and tryptase can be used as darkening agents. Furthermore, PAR-2 could be useful as a target for whitening and darkening agents.
We have further discovered that BBI, a Bowman-Birk type inhibitor, may also be used as an active depigmenting agent. Soybean-derived extracts and mixtures that were suggested in U.S. patent application Ser. No. 09/110,409 as depigmenting agents contain both STI and BBI. We have now found that BBI alone is effective to depigment skin. BBI may be used in all the formulations and compositions set forth in the parent application in the same range of concentration as STI.